BE-204 BASIC MECHANICAL ENGINEERING
BE (First/Second) Semester Examination June 2010
BE (First/Second) Semester Examination June 2010
(Common to all Branches)
Time: 3 hrs
Maximum Marks: 100
Minimum Marks: 35
Note: Attempt any five questions. Internal choices are given. Steam table is permitted.
1. (a) What are the effects of the
following elements of steel? 10 marks
(i) Chromium
(ii) Manganese
(iii) Molybdenum
(iv) Cobalt
(v) Sulphur
Ans: Refer article 1.5 Page 5 of BME - Basant Agrawal, Wiley India
Manganese: Manganese
increases hardenability and tensile strength of steel, but to a lesser extent
than carbon. It is also able to decrease the critical cooling rate during
hardening, thus increasing the steels hardenability much more efficient than any
other alloying elements. Manganese also tends to increase the rate of carbon
penetration during carburizing and acts as a mild deoxidizing agent. However
when too high carbon and too high manganese accompany each other, embrittlement
sets in. Manganese is capable to form Manganese Sulphide (MnS) with sulphur,
which is beneficial to machining. At the same time, it counters the brittleness
from sulphur and is beneficial to the surface finish of carbon steel.
Sulphur: Sulphur improves
machinability but lowers transverse ductility and notched impact toughness and
has little effects on the longitudinal mechanical properties. Its content is
limited to 0.05% in steels but is added to freecutting steels in amount up to
0.35% with the manganese content increased to counter any detrimental effects
since sulphur is beneficial to machining. For welding, weldability decreases
with increasing sulphur content. Sulphur is detrimental to surface quality in
low carbon and low manganese steels and it promotes hot shortness in welding
with the tendency increasing with increased sulphur.
1. (b) Define the following properties of engineering
material: 10 marks
(i) Proportionality limit
(ii) Resilience
(iii) Creep
(iv) Brittleness
(v) wear
Ans: Refer article 2.1 pages 12 of BME - Basant Agrawal, Wiley India
Proportionality limit: The proportional limit
is the point on a stress-strain curve where the linear, elastic
deformation region transitions into a non-linear, plastic deformation
region. In other words, the proportional limit determines the greatest stress that is directly proportional to strain.
Wear: Wear is the damaging, gradual removal or deformation of material at solid surfaces. Wear in machine elements, together with other processes such as fatigue and creep, causes functional surfaces to degrade, eventually leading to material failure or loss of functionality.
Or2. (a) Give
the composition properties and uses of wrought iron. 10 marks
Ans: The modern functional equivalent of wrought iron is mild steel, also called low-carbon steel. Wrought iron is no longer produced on a commercial scale. Many products described as wrought iron are actually made of low carbon steel. They retain that description because they are made to resemble objects which in the past were wrought (worked) by hand by a blacksmith.
Refer Page article 1.4 pages 4 of BME - Basant Agrawal, Wiley India
2. (b) Draw
the stress-strain curve for mild steel. Also discuss the various properties of
mild steel related to this curve. 10 marks
Ans: Draw Fig 7 of Page 17 and refer article 2.5, BME - Basant Agrawal, Wiley India
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3. (a) Explain
the various drilling operations done by drilling machine. 10 marks
Ans: Refer article 6.2 pages 101 of BME - Basant Agrawal, Wiley India
Or3. (b) Find
out the taper angle of workpiece if consecutive height of the two ends of a
sine bar from the surface plate is given as 10 cm and 5 cm. The length of sine bar
is 10 cm. 10 marks
Ans: Refer article 5.6 pages 87 of BME - Basant Agrawal, Wiley India
sin θ = (h1-h2)/L = (10-5)/10 = 1/2 ====> θ = 30°
sin θ = (h1-h2)/L = (10-5)/10 = 1/2 ====> θ = 30°
4. (a) Explain
milling machines. 10 marks
Ans: Refer article 6.3 page 102 of BME - Basant Agrawal, Wiley India
4. (b) Explain
the various pressure measurement instruments. 10 marks
Ans: Refer article 4.2 page 46 and onwards of BME - Basant Agrawal, Wiley India
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5. (a) Describe
with sketch construction and working of Kaplan turbine. 10 marks
Ans: Refer article 8.4 pages 151 and 152 of BME - Basant Agrawal, Wiley India
5. (b) If 5 m3
of a certain oil weighs 40 kN, calculate the specific weight, mass density and relative
density of the oil. 10 marks
Ans: Refer Problem 1 pages 113 of BME - Basant Agrawal, Wiley India
Or 6. (a) Explain the function of the following
components of hydroelectric power plant: 10 marks
(i) Forebay
(ii) Draft tube
Ans: Refer Figure 19 page 154 of BME - Basant Agrawal, Wiley India
Draft tube: If reaction turbines are used, then draft tube is a necessary component
which connects turbine outlet to the tailrace. The draft tube contains
gradually increasing diameter so that the water discharged into the
tailrace with safe velocity. At the end of draft tube, outlet gates are
provided which can be closed during repair works.
6. (b) Distinguish between the
following: 10 marks
(i) Impulse and reaction turbine
(ii) Peak load plant and base load
plant.
Ans: Refer article 8.4 page 149 of BME - Basant Agrawal, Wiley India
Peak load plant and base load
plant: Electrical power demand fluctuates and falls on a daily basis, depending
on external factors such as weather, time, seasons, events and so on. Base load, also called continuous load,
is relatively stable and refers to the minimum amount of electrical
demand over a 24-hour period. It is simply the level that demand typically does not
fall below or the basic amount of energy that is always required. Peak load is the daily fluctuation of electricity use. It is usually lowest in the off hours (mid-night) and highest in the early evening. It is far less
predictable than base load, as it can spike when, for example, heating
or air conditioners are turned on. Due to high demand, peak electricity
is more expensive.
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Ans: Refer article 11.13 page 238 of BME - Basant Agrawal, Wiley India
7. (b) A pressure
cooker has 3 kg of steam at 5 bar pressure at 0.9 dry. What quality of heat be
rejected so as the quality of steam becomes 60% dry? 20 marks
Ans: Refer problem 26 page 206 of BME - Basant Agrawal, Wiley India
Or 8. (a) Write short notes on the following: 10 marks
(i) Latent heat Refer page 180 of BME - Basant Agrawal, Wiley India
(ii) Dryness fraction Refer page 182 of BME - Basant Agrawal, Wiley India
(iii) Boiler efficiency Refer page 229 of BME - Basant Agrawal, Wiley India
(iv) Equivalent evaporation Refer page 227 of BME - Basant Agrawal, Wiley India
(v) Super heat Refer page 183 (degree of superheat) of BME - Basant Agrawal, Wiley India
8. (b) Find
the change in internal energy when one kg of steam expands from 10 bar and 300°C
to 5 bar and 0.9 dry. Take Cps = 2.1 kJ/kg. 10 marks
Ans:
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9. (a) Why does
actual indicator diagram differ from theoretical diagram? Explain them. 10 marks
Ans: incomplete question, hopefully it is related to steam engine. Refer article 13.6 Page 279 of BME - Basant Agrawal, Wiley India.
9. (b) Discuss
the working of Otto engine. 10 marks
Ans: Refer article 14.5 Page 306 of BME - Basant Agrawal, Wiley India.
Or 10. (a) Explain
the Carnot cycle and its ideal efficiency. 10 marks
Ans: Refer article 14.4 Page 300 of BME - Basant Agrawal, Wiley India.
10. (b) Differentiate between the following: 10 marks (i) Two stroke and four stroke engine
(ii) SI and Cl engine
Ans: Refer article 15.7 and 15.8 Page 333-334 of BME - Basant Agrawal, Wiley India.
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